How does sleep consolidate memory? (Diekelmann & Born, 2010)

During sleep the brain replays and relocates the day's memories — reactivating them and moving them into long-term storage.

Diekelmann & Born (2010, Nature Reviews Neuroscience) describe the active systems consolidation account. During slow-wave sleep (SWS) — the deepest non-dream stage — recently formed memories in the hippocampus are spontaneously reactivated ("replayed") and gradually redistributed to the neocortex for durable storage. REM sleep (the dreaming stage) supports synaptic consolidation, stabilising the changes at the level of individual connections.

The behavioural payoff is well replicated: a period of sleep after learning improves later recall and protects the material from interference more than an equal amount of time spent awake. Sleep is not passive downtime for your memory — it's an active processing shift.